Driven turbochargers are an improvement over normal turbochargers since driven turbochargers (super-turbochargers) are powered by more than just the exhaust gas turbine, which reduces turbo-lag in boosted engines. One class of driven turbocharger that has seen much development work is the electric turbocharger, where an electric motor/generator is integrated on the turbo shaft, and can drive the turbo shaft quickly up to speed and extract extra energy from the turbo shaft.